Punching/deforming tool for a strapping unit

ABSTRACT

Using a punching tool for a strapping unit for producing an auxiliary-free connection of ends of a strapping band, the tool having a recess of different widths, in the case of which at least one section of a recess-bounding wall is provided with a rounded portion in the region of at least one change in width, on the one hand, the intention is to make a fixed closure between the band ends possible. On the other hand, the intention is for this tool to be produced as easily and cost-effectively as possible and, in addition, for uniform cutting forces to be made possible. For this purpose, it is proposed that the rounded portion is of circle-arc shape with a certain radius, and that the largest width of the recess is equal to or less than four times the radius of the wall.

[0001] The invention relates to a punching/deforming tool for astrapping unit for producing an auxiliary-free connection of ends of astrapping band, the tool having a recess of different widths, and atleast one section of the recess-bounding wall being provided with arounded portion in the region of at least one change in width. Theinvention additionally relates to a process for producing such a tool,and to the closure itself.

[0002] Strapping units by means of which a tensioned band loop can bepositioned around articles which are to be packaged have been known forsome time now. This takes place, in particular, for packaging andtransporting purposes. Strapping units with very different functionalprinciples, in particular, in relation to the connection of the two bandends, have become known in this context. The present invention relatesto strapping units in the case of which the band loop is closed bydeformation and the production of an incisions. A form fit is formedbetween the two band ends in this case. In the case of strapping unitsof the generic type, furthermore, the closure is produced by twointeracting tools of the strapping unit. The tools are fed onto the topside of the two bands, one tool from the side of one band and the othertool from the side of the other band. The two tools, usually referred toas punch and die, force the band ends, located one upon the other, intoa cavity of the die, the deformation taking place as a result.

[0003] It is known from the prior art that the recess of the die has itslargest extent in the band-running direction, the width of the recessusually changing a number of times in the longitudinal direction of therecess. The die is thus of a complicated shape which is optimized inrespect of the incisions which are to be achieved. It is usually soughtto achieve the sharpest possible edges and corners in the wall, theintention being for these to make it possible for the two band ends tointerlock to particularly good effect. It is also known, from DE-A 19 05145, for the width to be changed by way of a radius. This is intended toreduce the risk of injury stemming from a band closure.

[0004] It has been found, however, that it is precisely the known shapeswhich produce a fixed and permanent closure of the band ends which areparticularly difficult to produce. Up until now the recess of the diehas usually been produced by impact production methods.

[0005] A further problem which may arise in the case of such tools isthe frequently occurring non-uniform cutting force. Varying cuttingforces during a closure operation result in an individual using thecorresponding strapping unit having to apply forces of differentmagnitudes. However, this is regarded as disadvantageous.

[0006] The object of the invention is thus to make a fixed closurebetween the band ends possible, in the case of which the tools forproducing the closure can be produced as easily and cost-effectively aspossible and, in addition, make more uniform cutting forces possible.Nevertheless, the intention is also for the closure to have goodstrength properties.

[0007] This object is achieved according to the invention, in the caseof an apparatus of the type mentioned in the introduction, in that therounded portion is essentially of circle-arc shape with a certainradius, and in that the largest width of the recess is equal to or lessthan six times, but preferably equal to or less than four times theradius of the wall. The object is additionally achieved by a process asdescribed in claim 7.

[0008] As a measure according to the invention, one or more roundedportions are thus provided in the region of changes in width of theboundary wall of the recess. It has surprisingly been found, within thecontext of the invention, that such rounded portions contribute to amore uniform cutting force of the tool during the production of aclosure between two band ends. If, in order to produce the recess, useis made of a milling process which utilizes a cylindrical millingcutter, then it is particularly easy to produce radii.

[0009] The milling process is particularly economical if, according tothe invention, the at least one radius and certain dimensions of therecess are coordinated with one another. It is thus possible for thelargest width of the recess to be produced, in a particularlycost-effective manner, by the same tool as the radius, provided that thelargest width of the recess is no more than triple, preferably double,the diameter of the milling cutter. It is also a contributory factor tocost-effective production if the smallest width is equal to or greaterthan the diameter of the milling cutter and thus double the value of theradius of the recess. It is thus possible for the smallest width of therecess to be produced with, at most, two cutting paths.

[0010] In connection with the invention the term “width” is to beunderstood as a dimension, which is essentially parallel to theorientation of the (flat) surfaces of the band ends to be closed, andessentially orthogonal to the band-running direction. Further, with theterm “rounded portion” such directions of curvature are to be understoodwhich are also orientated essentially parallel to the (flat) surfaces ofthe band ends to be connected.

[0011] It has been found that the radius according to the invention ofthe recess and/or of the milling cutter should be selected from a rangeof from 1 mm to 2.5 mm, preferably from a range of from 1.3 mm to 2.0mm.

[0012] Further preferred configurations of the invention can be gatheredfrom the claims and the drawings.

[0013] The invention will be explained in more detail with reference toan exemplary embodiment illustrated, purely schematically, in thefigures, in which:

[0014]FIG. 1 shows a strapping unit of the generic type in which use ismade of a tool according to the invention;

[0015]FIG. 2 shows a closure produced by a tool according to theinvention;

[0016]FIG. 3 shows a perspective illustration of a punch according tothe invention and of a die according to the invention;

[0017]FIG. 4 shows a plan view of the die according to the inventionfrom FIG. 3;

[0018]FIG. 5 shows a milling cutter in a number of positions during aprocess for producing the die according to the invention from FIG. 4;and

[0019]FIG. 6 shows a milling cutter in a number of positions during aprocess for producing the punch according to the invention from FIG. 3.

[0020] The manually actuated strapping unit 1 shown in FIG. 1 is anexample of strapping units of the generic type at which the invention isdirected. The strapping unit has a base plate 2, by means of thepreferably planar underside of which the strapping unit is positioned onan article which is to be strapped. A single-part punch 3 is fastened inthe base plate 2. A single-part die 4 which interacts with the punch 3is fastened in a releasable manner in a die carrier 5. The die carrier 5is articulated in a pivotable manner by means of a rotary articulation6, which is arranged at a front end of the base plate 2 (and of whichthe pivot axis 8 is illustrated). By means of a pivoting lever 7, thedie carrier 5 can be pivoted about the pivot axis 8 in the direction ofthe base plate 2 and raised off from the latter again. The pivot axis 8here is oriented essentially orthogonally to a band-running direction 9.During production of a strapping arrangement, the two band ends 10, 11are located one above the other in the band-running direction 9 betweenthe base plate 2 and the die carrier 5, in order then subsequently to beconnected to one another.

[0021] During lowering, the punch 3, together with the two band layers,penetrates into a recess which belongs to the die 4, and will beexplained in more detail hereinbelow, this resulting in the formation ofa closure 15 of two ends 10, 11 of a steel band, this closure beingshown in FIG. 2. In this case, one tool part approaches the two bandends 10, 11 from above, while the other tool part is arranged in astationary manner beneath the two band ends 10, 11. Since it is usuallythe case with such strapping units that the pivoting radius isrelatively large in comparison with the magnitude of the stroke movementof the die, the die 4 moves at least more or less rectilinearly in thedirection of the punch 3. Prior to this closure operation, a variouslyknown tensioning mechanism of the strapping unit 1 has been actuated bymeans of a tensioning lever 18 (FIG. 1), as a result of which, in turn,a band loop around an article which is to be packaged has beentensioned.

[0022] The punch 3 and die 4 here produce, by incisions and deformation,a region 20, shown in FIG. 2, in the two band ends 10, 11 which acts asa closure of the band ends 10, 11. This results in the band endsinterlocking, which is basically known per se, in particular in theband-running direction. This permanently prevents the band ends frombeing released in an undesired manner.

[0023]FIG. 3 shows a die 4 according to the invention and a mating punch3 of a punching tool. Both the die and the punch have bores 23, 24, 25which serve for fastening the two tool parts, inter alia, by means ofscrews 26, on the base plate 2 and the die carrier 5 of FIG. 1. The dieis provided with a recess 27 which is bounded by two walls 28. The walls28 have an undulating top side 28a in the direction of the punch 3. Awall surface 29 formed by the two walls 28 here bounds the recess 27.The contour or the profile of the wall surface 29 here corresponds to anouter contour 30 of the punch 3. The latter may thus penetrate into therecess 27 of the die 4, a small gap of essentially constant magnitudebeing produced here between the punch and the wall.

[0024] As can be gathered both from FIG. 3 and from FIG. 4, the die 4 isof a more or less cuboidal basic shape. The groove-like recess 27 runsover the entire length of the die 4 and is open in each case in thedirection of the two end sides of the latter. The recess 27, inaddition, runs parallel to the longitudinal extent of the die 4 and thusalso parallel to the band-running direction 9. The recess 27 hasessentially identical sections 32, 33 with two different width ranges.The exemplary embodiment of FIG. 4 provides in each case three sections32 with a width range B_(1min) equal to 3.2 mm to B_(1max) equal to 3.8mm, on the one hand, and three sections with the constant width B₂ of 6mm on the other hand. A section of one width range B₁ is followed ineach case by a section of the other width B₂. This periodicity isrepeated three times. The sections 32, 33 are of essentially equallength in the band-running direction 9, which is also indicated in FIG.4. The section with the smaller width range 32 tapers linearly in eachcase from a width B_(1max) to a width B_(1min).

[0025] The two regions B₁, B₂ are connected to one another by transitionlocations 34, 35. In contrast to the two regions 32, 33, the wallsurface and/or tangents to the transition locations 34, 35 are at arelatively large angle α to the band-running direction or an axis ofsymmetry 36 of the recess, which is identical to the band-runningdirection. In the exemplary embodiment, the angle α may be 45° or more.The transition locations 34, 35 here run into the sections 33, with thelarger of the two width ranges, with a radius R₁ of 1.55 mm and aconcave circle-arc shape. A concave arc with a radius R₂ of 1.55 mmlikewise immediately adjoins the end of the sections 33, as aconstituent part of the transition location 35. The transitions to andfrom the sections 32 are also provided with a respective radius R₃, R₄.These constituent parts of the convex transitions 34, 35 of circle-arcshape with a radius R₃, R₄ of likewise, in each case, 1.55 mm.

[0026] As can be gathered from FIG. 3, the punch 3 is shaped congruentlywith the recess 27 of the die and is essentially a negative image of therecess 27. The punch 3 thus likewise has sections with two differentwidths, the transitions to the larger width each also being providedwith the same radii.

[0027] In order to produce the die 4 according to the invention which isillustrated in FIGS. 3 and 4, use is made of an end-milling cutter 38which cuts along its circumference and on its end side and has a radiusof 1.55 mm. The milling cutter 38, which is illustrated in section inFIG. 5, may be guided along two cutting paths 39, 40, in the case ofwhich the centre axis of the milling cutter 38 is displaced in each caseparallel to the desired contour of the wall surface 29 which is to beproduced. The entire wall surface 29 can be produced by means of justthese two cutting paths 39, 40. A penetration depth of the millingcutter 38 here corresponds to the height of the wall surface 29. Sinceboth the width B_(1max) and B_(1min) of the narrower locations of therecess, and the width B₂ of the wider locations are, at most, equal todouble the diameter D of the milling cutter 38, it is also possible forthe entire recess 27 to be produced by means of these two cutting pathsalone.

[0028] In a further embodiment according to the invention, which is notillustrated, it is also possible for the largest width of thelarger-width section to be more than double the diameter of the millingcutter. The largest width, however, should correspond to not more thanthree times the diameter of the milling cutter 38 and thus six times theradius R₁. In this case, it is possible for the material which stillremains in the recess to be removed in the band-running direction by wayof a third cutting path. The third cutting path may lead through thealready produced sections with a smaller width range than non-productivecuts.

[0029] According to FIG. 6, the punch may be produced from a cuboidalblock, in the case of which the two longitudinal sides 30 of the punchare to be produced by means of the same milling cutter 38.

[0030] It can be gathered from FIG. 2 that a closure produced by apunching tool according to the invention has a deformed region 20provided with punched incisions. This region 20 contains in the bandends 10, 11, sub-regions 32′, 33′ which are essentially an image of thesections 32, 33 of the punching tool. This means that it is also thecase that the closure, on the one hand, contains, on itspunched/deformed outer edges, radii R₁′- R₄′ which essentiallycorrespond to the radii R₁-R₄.

[0031] On the other hand, the deformed/punched sub-regions 32′, 33′ alsohave widths B_(1min)′, B_(1max)′ and B₂′ which have at least more orless the same values as the respectively corresponding widths B_(1min),B_(1max) and B₂ of the tool.

1. Punching tool for a strapping unit for producing an auxiliary-freeconnection of ends of a strapping band, the tool having a recess ofdifferent widths, and at least one section of the recess-bounding wallbeing provided with a rounded portion in the region of at least onechange in width, characterized in that the rounded portion is ofcircle-arc shape with a certain radius (R₁, R₂, R₃, R₄), and in that thelargest width (B₂) of the recess (27) is equal to or less than six timesthe radius (R₁, R₂, R₃, R₄) of the wall (28).
 2. Punching tool accordingto claim 1, characterized in that the largest width (B₂) of the recess(27) is equal to or less than four times the radius (R₁, R₂, R₃, R₄) ofthe wall (28).
 3. Punching tool according to one or both of thepreceding claims , characterized in that the smallest width (B_(1min))of the recess (27) is at least double the radius (R₁, R₂, R₃, R₄) of thewall (28).
 4. Punching tool according to one of the preceding claims,characterized in that the boundary wall (28) is symmetrical in relationto a longitudinally running axis (26) of the recess (27).
 5. Punchingtool according to one of the preceding claims, characterized in that theradius (R₁, R₂, R₃, R₄) is selected from a range of from 1 mm to 2.5 mm.6. Punching tool according to one of the preceding claims, characterizedby a recess (27) which is produced using a milling process.
 7. Processfor producing a die of a strapping unit, by means of which it ispossible to produce an auxiliary-free closure between ends of astrapping band, a recess being made in the die, characterized in thatthe recess (27) is produced by milling and its boundary wall (28) isprovided with at least one rounded portion (R₁, R₂, R₃, R₄)
 8. Processaccording to claim 7, characterized in that the smallest width(B_(1min)) is produced in the recess (27) in a direction transverse to alongitudinal direction (9) of the recess (27), the smallest width(B_(1min)) corresponding at least to double a radius (R₁, R₂, R₃, R₄) ofthe rounded portion.
 9. Process according to claim 7 or 8, characterizedin that the largest width (B₂) is produced in the recess (27) in adirection transverse to a longitudinal direction (9) of the recess, thelargest width corresponding at most to six, preferably to four times aradius (R₁, R₂, R₃, R₄) of the rounded portion.
 10. Process according toone of the preceding claims 7 to 9, characterized in that a cylindricalmilling cutter (38) is utilized in order to produce the rounded portion,a diameter (D) of the milling cutter (38) corresponding to the value ofa radius (R₁, R₂, R₃, R₄) of the rounded portion of the boundary wall.11. Auxiliary-free closure of two band ends of a band strappingarrangement, the closure being produced by means of a punch and a die ofa strapping unit by way of a punching/deforming operation and beingformed as a punched/deformed region of the two band ends located oneabove the other, characterized by at least one deformed and/or punchedsub-region of the region (20), with the largest width, in relation to adirection perpendicular to the band-running direction (9), being lessthan or equal to six, preferably to four times a radius (R₁′- R₄′),which the punched/deformed region has on one of its outer edges.